The microbial ecology of soybean soaking for tempe production

Soybeans soaked in tap water for 24 to 36 h at 20, 30 or 37 degrees C underwent a natural fermentation that was characterized by the growth of microorganisms to 10(8)-10(10) cfu/ml (depending on temperature) and a reduction of pH from 6.5 to 4.5. Lactobacillus casei, Streptococcus faecium, Staphylococcus epidermidis and Streptococcus dysgalactiae dominated the fermentation but, significant contributions were also made by Klebsiella pneumoniae, Klebsiella ozaenae, Enterobacter cloacae, Enterobacter agglomerans, Citrobacter diversus and Bacillus brevis, and the yeasts Pichia burtonii, Candida didensiae and Rhodotorula rubra. Fermentation of surface-decontaminated beans in sterile water with pure cultures of these isolates showed L. casei, Strep. faecium and Staph. epidermidis to be the main species responsible for the pH reduction. Soybeans were the main source of microorganisms for the fermentation. Boiled beans did not undergo an acid fermentation.